【Media Foundation】简单实例 - 使用Media Session来播放文件

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参考MSDN官方的页面：http://msdn.microsoft.com/en-us/library/ms703190(v=vs.85)

本文详细演示了如何使用Media Foundation中的Media Session对象来播放媒体文件。也就是不自己编写/自定义任何的Media Foundation组件，一切都是用现成的，以及让Media Foundation“自动完成”的（如Topology的解析）。Media Foundation的API会根据文件的路径或URL智能创建合适的media source组件，并会智能地在media source和音视频渲染器(renderer)之间添加合适的解码器等等。Topology中的数据流等任务由Media Session来处理。

这是最简单的开发任务。然而，如果要实现使用自定义的meida source或media transform组件这样的任务，可能不能使用Media Session。

预备知识

在阅读本主题之前，你需要熟悉以下MF概念：

• Media Session
• Source Resolver
• Topologies
• Media Event Generators
• Presentation Descriptors

注意：此主题不描述如何播放被DRM保护的文件。关于MMF中DRM的相关信息，见 How to Play Protected Media Files。

其实不太了解以上概念也没关系，通过这个小例子的动手实践，我们会对一些基本概念有个基本了解。

概述

以下对象用来和Media Session播放多媒体文件：

• media source对象用来解析多媒体文件或其他媒体数据源。media source为文件中的每个音频或视频流创建一个steam对象。 Decoders把编码后的多媒体数据转换为非压缩视频和音频
• Source Resolver从URL创建一个media source
• EVR将视频渲染到屏幕上
• SAR将音频渲染至扬声器或其他音频输出设备
• Topology定义从media source至EVR和SAR的数据流
• Media Session控制数据流，并发送状态数据到应用程序。下图展示了这个过程

step by step实例

大概了解一下概念，我们可以来进行实践了。我们主要将完成以下任务：

• Media Foundation平台的初始化与关闭
• 创建media session
• 根据文件路径，（智能）创建（合适的）media source
• 创建topology，添加media source、EVR/SAR（renderer）节点，并将其连接，此时的topology是一个partial topology
• 将刚创建的topology关联到media session，内部的topology loader会给partial topology“智能地”加入所需的解码器等节点，使其成为一个complete topology
• 获取和处理来自media session的事件
• 用media session来控制播放，但不要直接操作media source
• 程序结束，释放资源

1. 创建程序

我使用visual studio 2012创建了一个基于对话框的MFC项目。含有可缩放的边框、 最小化框。

再创建一个菜单，把对话框的菜单属性设为此菜单。

添加全局的播放核心类对象 

Core*g_pCore = NULL;

在stdafx.h中添加要用到的头文件和类模板。头文件后面的注释说明了为什么需要它

#include <mfapi.h>// MFStartup, mfplat.lib#include <mfidl.h>// MFCreateMediaSession, mf.lib#include <evr.h>// IMFVideoDisplayControl, strmiids.lib#include <shlwapi.h>// QITABENT, shlwapi.lib#include <mferror.h>// MF_E_ALREADY_INITIALIZEDtemplate <class T> void SafeRelease(T **ppT){    if (*ppT)    {        (*ppT)->Release();        *ppT = NULL;    }}#include "Core.h" // Core类头文件

配置项目属性，此项目需要链接以下Lib:

mfplat.lib; mf.lib; mfuuid.lib; strmiids.lib; shlwapi.lib

2. 创建播放核心类Core

首先定义播放事件标识和播放状态的枚举

const UINT WM_APP_PLAYER_EVENT = WM_APP + 1;enum PlayerState{    Closed = 0,     // No session.    Ready,          // Session was created, ready to open a file.    OpenPending,    // Session is opening a file.    Started,        // Session is playing a file.    Paused,         // Session is paused.    Stopped,        // Session is stopped (ready to play).    Closing         // Application has closed the session,                    // but is waiting for MESessionClosed.};

此类被设计为单例模式（singleton），为了处理事件方便，它继承自IMFAsyncCallback接口，此接口又继承自IUnknown接口。因此我们要为Core类实现这些接口的所有必需方法。

类声明：

class Core : public IMFAsyncCallback{protected:Core(HWND hVideo);virtual ~Core(void);public:static HRESULT CreateInstance(HWND hVideo, Core** ppCore);// IUnknown方法STDMETHODIMP QueryInterface(REFIID iid, void** ppv);STDMETHODIMP_(ULONG) AddRef();STDMETHODIMP_(ULONG) Release();// IMFAsyncCallback方法STDMETHODIMP GetParameters(DWORD*, DWORD*){ return E_NOTIMPL;}STDMETHODIMP Invoke(IMFAsyncResult* pAsyncResult);HRESULT Initialize();HRESULT OpenFile(PCWSTR sURL);HRESULT HandleEvent(UINT_PTR pEvent);PlayerState GetState() const { return m_state; }BOOLHasVideo() const { return (m_pVideoControl != NULL); }HRESULT StartPlay();HRESULT Play();HRESULT Pause();HRESULT Stop();HRESULT Shutdown();HRESULT Repaint();HRESULT ResizeVideo(WORD width, WORD height);HRESULT OnTopologyStatus(IMFMediaEvent*);HRESULT OnPresentationEnded(IMFMediaEvent*);private:longm_nRefCount;PlayerStatem_state;IMFMediaSession*m_pMediaSession;IMFMediaSource*m_pMediaSource;IMFVideoDisplayControl* m_pVideoControl;HWNDm_hwndVideo;HANDLEm_hCloseEvent;};

构造函数、接口以及初始化等函数的实现， Event句柄m_hCloseEvent用来设置播放关闭时的标志，m_hwndVideo就是播放用的视频窗口，我设为主对话框的客户窗口，m_pVideoControl是一个IMFVideoDisplayControl接口指针，用来完成播放窗口相关的控制，如调整尺寸和重绘：

Core::Core(HWND hVideo) :m_pMediaSession(NULL),m_pMediaSource(NULL),m_pVideoControl(NULL),m_hwndVideo(hVideo),m_hCloseEvent(NULL),m_state(Closed),m_nRefCount(1){}Core::~Core(void){if(m_pMediaSession){Shutdown();}}HRESULT Core::QueryInterface(REFIID riid, void** ppv){    static const QITAB qit[] =     {        QITABENT(Core, IMFAsyncCallback),        { 0 }    };return QISearch(this, qit, riid, ppv);}ULONG Core::AddRef(){return InterlockedIncrement(&m_nRefCount);}ULONG Core::Release(){ULONG uCount = InterlockedDecrement(&m_nRefCount);if(uCount == 0)delete this;return uCount;} HRESULT Core::CreateInstance(HWND hVideo, Core** ppCore){if(hVideo == NULL)return E_UNEXPECTED;if(ppCore == NULL)return E_POINTER;Core* pCore = new Core(hVideo);if(pCore == NULL)return E_OUTOFMEMORY;HRESULT hr = pCore->Initialize();if(SUCCEEDED(hr)){*ppCore = pCore;(*ppCore)->AddRef();}SafeRelease(&pCore);return hr;}HRESULT Core::Initialize(){if(m_hCloseEvent)return MF_E_ALREADY_INITIALIZED;HRESULT hr = MFStartup(MF_VERSION);if(FAILED(hr))return hr;m_hCloseEvent = CreateEvent(NULL, FALSE, FALSE, NULL);if(m_hCloseEvent == NULL)hr = HRESULT_FROM_WIN32(GetLastError());return hr;}

3. 打开文件时的处理

这是一个核心的部分，代码较多，为了简单，我把所有代码都写到一个函数里去了，主要是为了理解方便。
主要完成了以下工作：

• 创建media session
• 开始从media session取得事件，开启播放相关事件的流动
• 根据文件路径创建合适的media source
• 创建partial topology
• 为media source的各个选定(selected)流创建source节点和renderer节点，将它们添加到partial topology并相互连接
• 将partial topology与media session关联，将partial topology解析成完整可用的topology

HRESULT Core::OpenFile(PCWSTR sURL){assert(m_state == Closed || m_state == Stopped);// 创建Media SessionHRESULT hr = MFCreateMediaSession(NULL, &m_pMediaSession);if(FAILED(hr))return hr;m_state = Ready;// 开始从Media Session取得事件hr = m_pMediaSession->BeginGetEvent((IMFAsyncCallback*)this, NULL);if(FAILED(hr))return hr;// 创建Media SourceIMFSourceResolver* pSourceResolver = NULL; IUnknown* pUnknown = NULL;IMFTopology* pTopology = NULL;IMFPresentationDescriptor* pPD = NULL;MF_OBJECT_TYPE objType = MF_OBJECT_INVALID;SafeRelease(&m_pMediaSource);hr = MFCreateSourceResolver(&pSourceResolver);if(FAILED(hr))goto over;// 为简单，弄成同步方法hr = pSourceResolver->CreateObjectFromURL(sURL, MF_RESOLUTION_MEDIASOURCE,NULL,&objType,&pUnknown);if(FAILED(hr))goto over;hr = pUnknown->QueryInterface(IID_PPV_ARGS(&m_pMediaSource));if(FAILED(hr))goto over;// 创建Topologyassert(m_pMediaSession != NULL);assert(m_pMediaSource != NULL);DWORD cStreams = 0;hr = MFCreateTopology(&pTopology);if(FAILED(hr))goto over;// 创建PresentationDescriptorhr = m_pMediaSource->CreatePresentationDescriptor(&pPD);if(FAILED(hr))goto over;// 获取source中的stream数目hr = pPD->GetStreamDescriptorCount(&cStreams);if(FAILED(hr))goto over;assert(pTopology != NULL);// 为每个stream创建topology节点，并将其加入到topologyfor(DWORD i = 0; i<cStreams; i++ ){        IMFStreamDescriptor* pSD = NULL;IMFTopologyNode* pSourceNode = NULL;IMFTopologyNode* pOutputNode = NULL;BOOL bSelected = FALSE;hr= pPD->GetStreamDescriptorByIndex(i, &bSelected, &pSD);if(FAILED(hr)) goto over2;if(bSelected){// source nodehr = MFCreateTopologyNode(MF_TOPOLOGY_SOURCESTREAM_NODE, &pSourceNode);if(FAILED(hr))goto over2;hr = pSourceNode->SetUnknown(MF_TOPONODE_SOURCE, m_pMediaSource);if(FAILED(hr))goto over2;hr = pSourceNode->SetUnknown(MF_TOPONODE_PRESENTATION_DESCRIPTOR, pPD);if(FAILED(hr))goto over2;hr = pSourceNode->SetUnknown(MF_TOPONODE_STREAM_DESCRIPTOR, pSD);if(FAILED(hr))goto over2;// output nodeIMFMediaTypeHandler* pHandler = NULL;IMFActivate* pRendererActivate = NULL;GUID guidMajorType = GUID_NULL;DWORD id = 0;pSD->GetStreamIdentifier(&id); // 忽略错误hr = pSD->GetMediaTypeHandler(&pHandler);if(FAILED(hr))goto over3;hr = pHandler->GetMajorType(&guidMajorType);if(FAILED(hr))goto over3;hr = MFCreateTopologyNode(MF_TOPOLOGY_OUTPUT_NODE, &pOutputNode);if(FAILED(hr))goto over3;if(MFMediaType_Audio == guidMajorType)hr = MFCreateAudioRendererActivate(&pRendererActivate);else if(MFMediaType_Video == guidMajorType)hr = MFCreateVideoRendererActivate(m_hwndVideo, &pRendererActivate);elsehr = E_FAIL;if(FAILED(hr))goto over3;hr = pOutputNode->SetObject(pRendererActivate);if(FAILED(hr))goto over3;// 把source节点和输出节点添加到topology，并连接它们hr = pTopology->AddNode(pSourceNode);if(FAILED(hr))goto over3;hr = pTopology->AddNode(pOutputNode);if(FAILED(hr))goto over3;hr = pSourceNode->ConnectOutput(0, pOutputNode, 0);over3:SafeRelease(&pRendererActivate);SafeRelease(&pHandler);goto over2;}over2:SafeRelease(&pSD);SafeRelease(&pSourceNode);SafeRelease(&pOutputNode);}hr = m_pMediaSession->SetTopology(0, pTopology);if(FAILED(hr))goto over;m_state = OpenPending;over:if(FAILED(hr))m_state = Closed;SafeRelease(&pPD);SafeRelease(&pTopology);SafeRelease(&pSourceResolver);SafeRelease(&pUnknown);return hr;}

主对话框需要提供一个文件/打开菜单，用来打开文件，它的响应如下。由于IMFSourceResolver::CreateObjectFromURL方法只支持LPCWSTR类型的文件路径字符串参数，所以当我们以多字节配置build程序时，需要添加代码，把打开文件对话框取得的多字节文件路径字符串转换成宽字符串。

void CBlackPlayerDlg::OnOpen(){HRESULT hr = S_OK;TCHAR path[MAX_PATH];path[0] = _T('\0');OPENFILENAME ofn;::ZeroMemory(&ofn, sizeof(ofn));ofn.lStructSize = sizeof(ofn);ofn.hwndOwner = this->GetSafeHwnd();ofn.lpstrFilter = _T("Media Files\0*.asf;*.avi;*.mp3;")                          _T("*.mp4;*.wav;*.wma;*.wmv\0All files\0*.*\0");ofn.lpstrFile = path;ofn.nMaxFile = MAX_PATH;ofn.Flags = OFN_FILEMUSTEXIST;ofn.hInstance = AfxGetInstanceHandle();if(::GetOpenFileName(&ofn)){#ifdef UNICODEhr = g_pCore->OpenFile(ofn.lpstrFile);#elsesize_t cLen = 0, cChars = 0;cLen = _tcslen(ofn.lpstrFile);WCHAR wstr[MAX_PATH*2] = {L'\0'};::MultiByteToWideChar(CP_ACP, 0, ofn.lpstrFile, -1, (LPWSTR)wstr, MAX_PATH);hr = g_pCore->OpenFile(wstr);#endifif(SUCCEEDED(hr)){UpdateUI(g_pCore->GetState());}else{AfxMessageBox(_T("无法打开文件！"));}}}

4. 处理media session事件

第3步代码的开头我们已经使用BeginGetEvent方法开始获取Media Session的事件，这是一个异步方法，当下一个事件发生时，media session会调用IMFAsyncCallback::Invoke方法。注意此方法是在worker线程调用的，不是主程序所在线程，所以这方法必须线程安全。

HRESULT Core::Invoke(IMFAsyncResult* pResult){MediaEventType meType = MEUnknown;IMFMediaEvent* pEvent = NULL;// 从事件队列中获取事件HRESULT hr = m_pMediaSession->EndGetEvent(pResult, &pEvent);if(FAILED(hr))goto over;// 取得事件的类型hr = pEvent->GetType(&meType);if(FAILED(hr))goto over;if(meType == MESessionClosed){::SetEvent(m_hCloseEvent);}else{hr = m_pMediaSession->BeginGetEvent(this, NULL);if(FAILED(hr))goto over;}if(m_state != Closing){pEvent->AddRef();::PostMessage(m_hwndVideo, WM_APP_PLAYER_EVENT, (WPARAM)pEvent, (LPARAM)0);}over:SafeRelease(&pEvent);return S_OK;}

Invoke方法中，我们先用EndGetEvent取得事件，接着用PostMessage将此事件发送给主程序窗口，其实主窗口还是把它送回给了Core的HandleEvent方法来进行实际处理。还要再次调用BeginGetEvent方法来异步获取下一事件。所以主对话框类要添加WM_APP_PLAYER_EVENT事件的处理程序：

afx_msg LRESULT CBlackPlayerDlg::OnPlayerEvent(WPARAM wParam, LPARAM lParam){HRESULT hr = S_OK;hr = g_pCore->HandleEvent(wParam);if(FAILED(hr))AfxMessageBox(_T("事件处理发生错误！"));UpdateUI(g_pCore->GetState());return 0;}

以下是Core类的HandleEvent，还可以根据需要添加更多的事件处理：

HRESULT Core::HandleEvent(UINT_PTR pEventPtr){HRESULT hrStatus = S_OK;HRESULT hr = E_FAIL;IMFMediaEvent* pEvent = NULL;IUnknown* pUnk = (IUnknown*)pEventPtr;if(pUnk == NULL)return E_POINTER;hr = pUnk->QueryInterface(IID_PPV_ARGS(&pEvent));if(FAILED(hr))goto over;MediaEventType meType = MEUnknown;hr = pEvent->GetType(&meType);if(FAILED(hr))goto over;hr = pEvent->GetStatus(&hrStatus);if(FAILED(hr))goto over;if(FAILED(hrStatus)){hr = hrStatus;goto over;}switch(meType){case MESessionTopologyStatus:hr = OnTopologyStatus(pEvent);break;case MEEndOfPresentation:hr = OnPresentationEnded(pEvent);break;default:break;}over:SafeRelease(&pUnk);SafeRelease(&pEvent);return hr;}

相关的具体事件的处理方法 ：

HRESULT Core::OnTopologyStatus(IMFMediaEvent* pEvent){MF_TOPOSTATUS status;HRESULT hr = pEvent->GetUINT32(MF_EVENT_TOPOLOGY_STATUS, (UINT32*)&status);if(SUCCEEDED(hr) && (status == MF_TOPOSTATUS_READY)){SafeRelease(&m_pVideoControl);// 如果source没有视频stream，此方法将失败(void)MFGetService(m_pMediaSession, MR_VIDEO_RENDER_SERVICE,IID_PPV_ARGS(&m_pVideoControl));hr = StartPlay();}return hr;}HRESULT Core::OnPresentationEnded(IMFMediaEvent* pEvent){m_state = Stopped;return S_OK;}

5. 控制播放

构建好完整的topology、设置好事件处理之后，可以真正地开始播放了，以下是播放的一些相关代码：

// 从当前位置开始播放HRESULT Core::StartPlay(){PROPVARIANT varStart;PropVariantInit(&varStart);varStart.vt = VT_EMPTY;// start是异步方法HRESULT hr = m_pMediaSession->Start(&GUID_NULL, &varStart);if(SUCCEEDED(hr))m_state = Started;PropVariantClear(&varStart);return hr;}HRESULT Core::Play(){if(m_state != Paused && m_state != Stopped)return INET_E_INVALID_REQUEST;if(m_pMediaSession == NULL || m_pMediaSource == NULL)return E_UNEXPECTED;return StartPlay();}HRESULT Core::Pause(){if(m_state != Started)return INET_E_INVALID_REQUEST;if(m_pMediaSession == NULL || m_pMediaSource == NULL)return E_UNEXPECTED;HRESULT hr = m_pMediaSession->Pause();if(SUCCEEDED(hr))m_state = Paused;return hr;}HRESULT Core::Stop(){if(m_state != Started && m_state != Paused)return INET_E_INVALID_REQUEST;if(m_pMediaSession == NULL)return E_UNEXPECTED;HRESULT hr = m_pMediaSession->Stop();if(SUCCEEDED(hr))m_state = Stopped;return hr;}

视频render(EVR)在我们提供的视频窗口绘制视频图象，这发生在一个工作线程，一般不需要管它。但如果播放暂停或停止时，当视频窗口接收到WM_PAINT消息时，我们必须通知EVR，方法是调用IMFVideoDisplayControl::RepaintVideo方法：

HRESULT Core::Repaint(){if(m_pVideoControl)return m_pVideoControl->RepaintVideo();elsereturn S_OK;}

同时，我们还需要修改主对话框的OnPaint事件处理函数：

void CBlackPlayerDlg::OnPaint(){if (IsIconic()){// 略。。。。}else{if(g_pCore && g_pCore->HasVideo())g_pCore->Repaint();CDialogEx::OnPaint();}}

我们还需要让用户可以调整视频窗口大小，这通过IMFVideoDisplayControl::SetVideoPostition方法来完成：

HRESULT Core::ResizeVideo(WORD width, WORD height){if(m_pVideoControl){RECT rc = {0, 0, width, height};return m_pVideoControl->SetVideoPosition(NULL, &rc);}elsereturn S_OK;}

类似与重绘，我们也要相应修改主对话框类，为其添加WM_SIZE的消息处理程序：

void CBlackPlayerDlg::OnSize(UINT nType, int cx, int cy){CDialogEx::OnSize(nType, cx, cy);if(g_pCore != NULL && g_pCore->HasVideo())g_pCore->ResizeVideo(cx, cy);}

6. 结束后的清理

播放完成后我们需要做一些清理工作，比如析构函数中的ShutDown方法：

HRESULT Core::Shutdown(){HRESULT hr = S_OK;SafeRelease(&m_pVideoControl);if(m_pMediaSession){DWORD dwRet = 0;m_state = Closing;hr = m_pMediaSession->Close();if(FAILED(hr))goto over;dwRet = WaitForSingleObject(m_hCloseEvent, 3000);}// 以下shutdown都是同步方法，无事件if(m_pMediaSource)m_pMediaSource->Shutdown();if(m_pMediaSession)m_pMediaSession->Shutdown();SafeRelease(&m_pMediaSource);SafeRelease(&m_pMediaSession);m_state = Closed;MFShutdown();if(m_hCloseEvent){::CloseHandle(m_hCloseEvent);m_hCloseEvent = NULL;}over:return hr;}

我在对话框类的析构函数里添加：

CBlackPlayerDlg::~CBlackPlayerDlg(){if(g_pCore != NULL){g_pCore->Shutdown();g_pCore->Release();}}

7. 杂项

如果要用键盘的空格键控制视频的暂停/重新播放，主对话框类需要重载PreTranslateMessage函数：

// 必须直接重载此函数，直接处理WM_CHAR或WM_KEYUP消息不行BOOL CBlackPlayerDlg::PreTranslateMessage(MSG* pMsg){// TODO: 在此添加专用代码和/或调用基类if(g_pCore != NULL && pMsg->message == WM_KEYUP){if(pMsg->wParam == VK_SPACE){if(g_pCore->GetState() == Started)g_pCore->Pause();else if(g_pCore->GetState() == Paused)g_pCore->Play();}return TRUE;}return CDialogEx::PreTranslateMessage(pMsg);}

如果要添加个控制菜单，里面有暂停、停止，它们的响应如下：

void CBlackPlayerDlg::OnPause(){if(g_pCore != NULL){if(g_pCore->GetState() == Started)g_pCore->Pause();}}void CBlackPlayerDlg::OnStop(){if(g_pCore != NULL){if(g_pCore->GetState() == Started || g_pCore->GetState() == Paused)g_pCore->Stop();}}